1. Field of the Invention
The present invention relates to a centraliser. In particular, but not exclusively, the present invention relates to an expandable centraliser for locating a body within a borehole.
2. Description of the Related Art
In the oil and gas exploration and production industry, a borehole is drilled from surface to a desired depth and sections of tubular casing are coupled together, run into the borehole and cemented in position.
Typically, the well is drilled to a first depth and certain physical parameters checked, before the first section of well is lined with a casing string which extends from a wellhead and which is made up from sections of tubular casing coupled together. The well is then drilled to a greater depth, and a smaller diameter casing string is located extending from the wellhead within the first casing string and the unlined well section, and cemented in place. This procedure is continued until a final section of the borehole is lined with a tubular liner string extending from the bottom of the deepest casing string, to gain access to hydrocarbon bearing formations.
The casing and liner strings must be centralised within the open borehole to allow fluid circulation between the outer surface of the tubing string and the borehole, such that cement used to seal and fix the string into position can flow up the annulus defined between the borehole wall and the tubing string. This is achieved by locating centralisers at intervals along the strings.
Current centralisers include solid and sprung/wicker centralisers. Solid centralisers define a section of increased outer diameter on the respective tubing string and typically include spiral (helical) or straight (axial) bypass slots for fluid circulation. Sprung or wicker centralises include sprung wicker arms or strips spaced around the outer diameter of the tubing.
Recent developments in the industry include the use of expandable tubing, which offers a number of advantages over conventional downhole tubing. Proposals include running expandable tubing into a borehole in an unexpanded configuration and then expanding the tubing downhole. However, conventional centralisers cannot be expanded and cannot be used with expandable tubing.
It is amongst the objects of embodiments of the present invention to obviate or mitigate at least one of the foregoing disadvantages.